Show unavailable message if user is in disconnected state

[zenparsing]

Resolves brave/brave-browser#20991

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally: npm run test -- brave_browser_tests, npm run test -- brave_unit_tests, npm run lint, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Screenshots

Test Plan

• Open browser with a fresh profile.
• Enable Rewards and verify with an external wallet provider.
• Invalidate the authentication tokens for the wallet provider.
  • For Uphold, this can be accomplished by visiting your account page, clicking the "3 dots" more menu, and selecting "Integrations". The integration for "Brave Browser" can then be removed.
• Visit the NPT and verify that "login" messaging appears.
• Open the Rewards panel and verify that "login" messaging appears.
• Visit the Rewards page and verify that "login" messaging appears.
• Verify that clicking on the login messaging box will take the user to the wallet provider authorization page.

[szilardszaloki]

@zenparsing Do we want to handle the case where fetch balance returns with an error?

[zenparsing]

@szilardszaloki We do, I'll mark this as a draft until that's been added.

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[brave-builds]

A Storybook has been deployed to preview UI for the latest push

[szilardszaloki]

LGTM

[aguscruiz]

Everything looks great!

[bsclifton]

Tested - my account might be different (since it's older? or maybe Uphold changed the UI) but integrations showed for me in a weird "shapes" menu (instead of 3 dot menu):